Manufacture of monoammonium phosphate



N. C. LINDBERG ET AL MANUFACTURE OF MONOAMMONIUM PHOSPHATE Filed July 23, 1928 2.2023. jaZaZJZQ mm mw .Mwwww... ww m m Jan. 12, 1932.

Patented Jan. 12, 1932 UNITED `STATES PATENT OFFICE NILS C. `LINlDBEPuI AIiD' GUY A. MCDONALD, OF CHICAGO HEIGHTS, ILLINOIS, ASSIGNORS VICTOR CHEMICAL WORKS, A CORPORATION OF ILLINOIS MANUFACTURE OF MONOAMMONIUM PHOSPHATE Application led July 23, 1925. Serial No. 294,613.

This invention relates to the manufacture talsy by a washing or flotation operation. of phosphate compounds, and particularlyA Since the washinfr operation is mechanical in mono-ammonium phosphate.` action, any liquid which will not injure the k1When ammonium phosphate is produced desired crystals may be employed. Generalf, by reacting with ammonia upon weak phosly, an aqueous liquid is employed, and prefer- 55 phoric acid, that is, phosphoric acid of a ably an aqueous liquid which will not excesgravity of about 30 B., such as acid obsively dissolve the desired ammonium phostained yby the treatment of phosphate rock phate crystals. On this account mother with sulphuric acid, the iron and aluminum liquor, preferably filtered to remove undel phosphates are found to be relatively insired impurities, is highly suitable. The G0 soluble in the dilute solution of ammonium washing of the crystals can be eilected in any phosphate and can readily be removed theredesired manner and is preferably effected by from by filtration before concentration and causing the washing fluid to flow through the crystallization. crystals while the latter are being moved When using strong phosphoric acid, such progressively in the opposite direction. In 65 as is obtained by the Ivolatilization process, this way, the iron and aluminum phosphates which may have a strength of about 75% are floated olf in the liquid stream. and may contain around 0.5% of iron and The invention will more readily be underaluminum phosphates, it is found thatthe stood from the following description in conammonium phosphate solution produced by Junction with the accompanying drawing ,-0

supplying ammonia to such acid .appears to which shows, diagrammatica-lly, an apparahave a solvent action upon the aluminum and tus suitable for the operation of the process. f iron phosphates, so that they are not com- Referring to the accompanying drawing, pletely precipitated as in the case of weaker 10 is an ammonia still which is adapted to 3 solutions. Ammonium phosphate crystals supply ammonia vapors to an outlet 11 in an 75 produced from such solutions are contamiacid tank12, which is provided with a suitnated with iron and aluminum phosphates. able stirrer 13 and a valved outlet 14. The The iron and aluminum phosphates could ob- Yalved outlet 14 leads into a suitable crystalviously be largely removed by diluting `the lizer 15, which is shown, by way of example,

i ammonium phosphate solution so as to preas an elongated chamber provided internally so cipitate the iron and aluminum phosphates, with a helical conveying kscrew and exterfiltering toremove them, concentrating and nally with the water jacket for the purpose crystallizing. This procedurele expensive of reducing the temperature to cause the and, moreover, the'concentration would neeformation of crystals. The valved outlet 16 essarily be effected in lead vessels so that the of the crystallizer 15 feeds into a suitable S5 product would become contaminated with apparatuslTfOl" WSllIlg the Crystals. AS leed, f, shown in the drawing, a Dorr classifier may It has new been discovered that if Such be employed, but it must be understood that strong solutions of ammonium phosphate are any suitable apparatus which permits crysl crystallized, the iron and aluminum phostals to be moved in one direction, preferably 9o pilates can readily be removed from the amsomewhat upwardly, and permits washing monium phosphate Crystals by mechanical liquid to flow through the crystals in the opwashing. UThe ironv and aluminum phosposite direction, may be employed. For e2:- phates thus precipitated appear to. be of ample, an upwardly sloping screw conveyor amorphous character and diffe-r substantially has 4given satisfactory results. The washer 'J5 in density from the crystals` of ammonium 17 comprises a sloping plane 18 and a rake v phospate which are formed simultaneously. 19 which is adapted to be operated so as to @n account oftheir lower density the iron causey the crystals to move progressively up and aluminum phosphates are readily rethe plane. The pipe 16 preferably leads ymoved from the ammonium phosphate crysonto a lower part of the plane 18. The wash- 100 Yer is provided with sides 20 so as to cause a "body of liquid to collect about the lower part pliedy thereinto for the purpose hereinafter to be described. From the lower end of the tanks l22,'valved connections lead into a pipe 24 which isprovided with a pump 25 and is connected to a suitable filter pressV 26. The outlet of the filter press leads into a tank 27 from which a valved outlet 28 leads to the top of the inclined plane 18. The upper end of the plane 18 is provided with a hopper 29 for the reception of washed crystals. The hopper 29 leads into a container 30 provided with a perforated bottom 31, which permits liquid to drain therethrough into a receptacle 32 which communicates by pipe 33 into pipe 24. A pipe n 34 provided with a pump 35 leads from the bottom of the tank 27 into the tank 12. n

Incarrying out the process with strong,` phosphoric acid and ammonia vapor, it is necessary to dilute somewhat in order to obtain crystals in a form in which they may be readily handled. Owing t9 the heat of the reaction a certain amount of water is evaporated. f- According to the present process, the phosphoric acid is diluted with a suitable quantityof filtered mother liquor and conditions are adjusted so that approximately the same amount of water is evaporated during neutralization asis introduced with the acid and; with the ammonia vapor. In this way, thepformation and crystallization of th-e ammonium phosphate isreffected without the necessity of any evaporating step.

Ammoniu'm phosphate solution attacks iron to a certain extent and it is, therefore, preferred to avoid the/employment of iron in the apparatus as far as possible. rIhe method herein described provides means for the removal of such iron as may be dissolved.

The operation willr be more readily understood from the following specific example: 940 lbs. of 75% phosphoric acid are supplied tothe tank 12 and are diluted with about 81 gallons of cold saturated ammonium phosphate solution of a gravity of 24o B., which is supplied from tank 27 by pipe 34. Approximately 500 lbs. of 26% ammonia liquor is placed in still 10 and the ammonia is distilled into the mixture in the tank 12. The temperature of the finished batch is about 90 to 1000- G., and the density is approximately 42o B. During the neutralization a considerable amount of evaporation takes place, so that the amount of mother liquor obtained from the batch is substantially the same as the amount of ammonium phosphate solution whichwas used to dilute the acid.

kThe hot ammonium phosphate solution is now passed through the crystallizer 15, wherein it is cooled to about 20 to 25 C., agitated by the screw conveyor and fed thereby toward the outlet pipe 16 which carries it into the washing apparatus 17. VIn this apparatus, the crystals are moved upwardly over the inclined plane 18 and eventually pass into the hopper 29. In thus passing up the plane 18 they meet a countercurrent of saturated ammonium phosphate solution which is supplied'by pipe 28.` This solution mechanically Vwashes a large percentage of the iron and aluminum phosphates, from the crystals, and these amorphous phosphates remain suspended in the solution and pass by pipe 21 to either of the tanks 22.

In the tanks 22, the mother liquor is treated for `the oxidation of any ferrous phosphate which it" may contain and which may have been derived from the attack of the ammonium phosphate solution on iron, or may have been contained in the original acid. This oxidation is effected by supplying compressed air by pipe 23, which causes agitation of the mother liquor and at the same time oxidizes the ferrous phosphate to ferrie phosphate which is immediately precipitated. The mother liquor is then forced by pump 25 through the filter press 26, whereby the iron and aluminum phosphates are removed and substantially pure ammonium phosphate solu`- tion is passed into the tank 27 and used in diluting the acid in tank 12 and in washing the crystals in the washer 17 in the manner hereinbefore described. Y Y

From the hopper 29, the crystals pass into the container 30 and the adheringsolution drips into receptacle 32 from which it passes bypipe 33 into the filter press 26.Y

By this method, the content of iron and aluminum phosphates vin commercial ammonium phosphate derived from strong;r phosphoric acid cany be reduced from about 0.7 5% to about 0.04%. 1 Y Y While the invention has been particularly described with relation to ammonium phosphate. it must be understood that itis not intended to be limited to the production of ammonium phosphate, since other phosphate compounds, such as -sodium phosphatmetc.. may be obtained in a similar high degree of purity by this process.

It must also be understoodl that many changes and modifications may be made in the apparatus andthe method within the scope of the present invention. Itis particularly to be understood that the details of the specific embodiment and example which have been employed to describe the invention are not intended to be limitative upon the scope of the invention, except in so far as included in the terms of the accompanying claims.

lll

We claim: s

l. The method of producing phosphate compounds substantially free from iron and aluminum impurities, which consists in crystallizing a solution of such compounds ol such concentration as to contain such impurities in solution, whereby said impurities are thrown out of solution With the crystals, separating the crystals from the mother liquor and washing said crystals with mother liquor thereby mechanically removing iron and aluminum impurities therefrom.

2. The method of producing phosphate compounds substantially free from iron and aluminum impurities which consists in crystallizing a solution of such phosphates of such strength as to dissolve saidiron and aluminum impurities, whereby the iron and aluminum impurities are thrown out with the crystals, separating the crystals from the mother liquor, iltei'ing said mother liquor and washing said crystals with filtered mother liquor,

thereby mechanically removing iron and aluminum impurities therefrom.

3. The method of producing phosphate compounds substantially free from iron and aluminum impurities which consists in crystallizing a solution of phosphates containing such impurities, separating the crystals from the mother liquor, oxidizing and filtering said mother liquor and washing said crystals with filtered mother liquor, thereby mechanically removing iron and aluminum impurities therefrom.

4. The method of producing phosphates substantially free from iron and aluminum compounds which consists in diluting strong phosphoric acid with aqueous liquid, forming phosphates from said acid, crystallizing the mixture, separating the phosphate crystals from the mother liquor, and washing the crystals to mechanically remove iron and aluminum compounds therefrom, the amount of aqueous liquid used to dilute the strong acid being such that the amount of water evaporated by the heat of the reaction is approximately equal that contained in the acid and introduced with the salt forming compound.

5. The method of producing phosphates substantially free from iron and aluminum compounds which consists in diluting strong phosphoric acid with mother liquor, forming phosphates from said acid, crystallizing the mixture, separating the phosphate crystals from the mother liquor, filtering said mother liquor and washing the crystals with filtered mother liquor thereby mechanically removing iron and aluminum compounds, the amount of mother liquor used to dilute the acid being such that the amount of water evaporated by the heat of the reaction is approximately equal that contained in the acid and introduced with the salt forming compound.

6. Thevmethod `of producing mono-ammonium phosphate substantially free from iron and aluminum compounds, which consists in crystallizing a solution of such phosphates containing iron and aluminum compounds, which solution is of a strength such as to dissolve the iron and aluminum impurities, whereby the latter are thrown out of the solution with the phosphate crystals in segregable form, separating the crystals from the mother liquor and washing said crystals with mother liquor, thereby removing the precipitatald ironand aluminum impurities mechanica y.

7. The method of producing mono-ammonium phosphate substantially free from iron and aluminum compounds, which consists in crystallizing a solution of such phosphates containing iron and aluminum compounds, separating thel crystals from the mother liquor, oxidizing and filtering said mother liquor and washing said crystals with filtered mother liquor.

8. The method of producing mono-ammonium phosphate substantially free from iron for crystallization of phosphate forming and aluminum compounds which consists in supplying ammonia to strong phosphoric acid containing iron and aluminum compounds to form phosphate of ammonia, the concentration of the phosphoric acid being such that the iron and aluminum impurities remain in solution, crystallizing said phosphates whereby the iron and aluminum com- A pounds are thrown out with the crystals in segregable form and washing the crystals to remove the iron and aluminum compounds.

9. The method of producing mono-ammonium phosphate which consists in diluting strong phosphoric acid with aqueous liquid,

supplying 'ammonia to said diluted acid, crystallizing Ythe mixture, separating the mono-ammonium phosphate crystals from the mother liquor, washing lthe crystals with aqueous liquid to mechanically remove iron and aluminum compounds, the amount of aqueous liquid used to dilute the acid being` such that the amount of water is evaporated by the heat of reaction is approximately equal to the amount of water contained in the acid and supplied with the ammonia.

10. The method of producing mono-ammonium phosphate which consists in diluting strong phosphoric acid with mother liquor, 1

supplying ammonia. to said diluted acid, l

crystallizing the mixture, separating the mono-ammonium phosphate crystals from the mother liquor, filtering said mother liquor and washing the crystals with filtered mother liquor thereby mechanically removing iron and aluminum compounds, the amount of mother liquor used to dilute the acid being such that the amount of Water evaporated by the heat of the reaction is approximately vor equal to the amount of Water contained in the acid Sand supplied with the ammonia.

Ill. The method of producing mono-ammonium phosphate Which consists in diluting strong phosphoric acid With ltered mother liquor, supplying ammonia to said diluted acid, crystallizing the mixture, separating the mono-ammonium phosphate crystals from the mother liquor, oxidizing and filtering said mother liquor and Washing the crystals With filteredmother liquor, the amount of filtered mother liquor used to dilute the acid being such that the amount'of Water evaporated bytlie heat of the reaction is approximately-equal to that contained in the acid and supplied With the ammonia.

12.',Tlie method of Aproducing mono-ann:`

monium phosphate v substantially free'` from iron and aluminum compounds, from strong phosphoricfacid containing such compounds,

which consists in diluting 940 lbs. by Weight i of% phosphoric acidWith about 8l 'gah lons of cold saturated ammonium phosphate solution, y,distillingthe ammonia from about 500 lbs. of 26% ammonia into the mixture so Y that the temperature rises to about to 100 C. thereb7 evapoiating WaterV iii amount about equal to the Water contained in the acid and introduced With the ammonia, cooling the mixture to about 20 to 25 C. and crystallizing'the mono-ammonium phosphate, sepf Varating the mother liquor from the crystals,

passing air through the mother liquor to'oxidize -i'errous ycompounds filtering the oxidl ized mother liquor and mechanicallywashing the crystalswith filtered mother liquor. v 13. The method of producing phosphates substantially free from iron and aluminum impurities which :consists indiluting phosphoric acidcontaining such impurities and` having a gravity substantially above 300 B. so vasto provide suliicient liquid medium for crystallization of phosphates, forming phosphates from said acid, crystallizing the mixture, separating the crystals from the mother liquor, Washing the .crystals and thereby mechanically removing. the iron and aluminum impurities from the phosphatel crystals.

yIn testimony whereof We have hereunto set 9 our hands `and seals this 27th day of June,v

1928. NILS C. LINDlBERG.

GUY A. MCDONALD. 

